Multiple modulation heterodyne infrared spectroscopy

摘要

A heterodyne detection technique for highly localized IR spectroscopy based on an AFM. A pulsed IR source illuminates a sample and causes contact resonance of an AFM probe, which is a function of localized absorption. The probe is operated in intermittent contact mode and is therefore oscillated at a resonance frequency. A secondary oscillation is mixed in to the probe oscillation such that the sum of the secondary oscillation and the IR source pulse frequency is near another harmonic of the probe. A mixing effect causes measurable probe response at the other harmonic allowing data to be taken away from the pulse frequency.

主权项

1. A method of obtaining nanoscale measurements of optical absorption of a sample with an oscillating cantilever probe of a probe microscope and a source of infrared radiation, the method comprising:
modulating the infrared source at a frequency fm; illuminating a region of a sample with a beam from the modulated, infrared source of infrared radiation; oscillating the cantilever at a first frequency f1; modulating the tip-sample separation at at least one second frequency f2; and, detecting an oscillation of the cantilever at a frequency f2+nfm, where n in an integer.